1. Field of the Invention
The present invention relates to a device for treating ULSI semiconductors represented by Si wafers in a high-temperature, high-pressure atmosphere. More particularly, the invention relates to a device used for a treatment for eliminating pores mainly by means of inert gas pressure, such as a so-called pressure filling method (high-pressure reflow process) for wiring films by which wafers having wiring films formed therein are treated using inert gas pressure.
2. Description of the Related Art
One example of a known semiconductor wafer fabrication process including a high-pressure gas treatment is a so-called pressure filling method for wiring films (high-pressure reflow processes; disclosed in Japanese Unexamined Laid-Open Applications Nos. 2-205678, 3-225829, and 7-193063) in which wafers having aluminum alloy wiring films formed therein by a PVD method are treated using inert gas pressure.
Further, an example of a known semiconductor processing technique using a gas whose pressure is as high as several tens atm is a high-pressure oxidation process in which a dielectric layer is formed by oxidizing the surface of a Si wafer. Since this treatment is intended for oxidation, oxygen or water is inevitably mixed into a pressure medium.
It is known that the former process uses a so-called single wafer processing cluster tool type device by which semiconductor wafers are subjected to a PVD treatment and then to a high-pressure treatment one by one. As disclosed in Japanese Unexamined Patent Laid-Open Application No. 7-193063 (see FIG. 6 in the said publication), this device treats wafers by sequentially transferring the wafers in a lock chamber to a series of treating modules disposed around a core chamber using a transfer arm inside the core chamber. A high-pressure module directly installed to the core chamber has been proposed as one of the modules (Prior art 1). An example of a more detailed structure of this high-pressure module has also been proposed by the same applicant in Japanese Unexamined Patent Laid-Open Application No. 7-502376 (Prior art 2).
It is also known that the latter process, particularly a process performed in an atmosphere of high-pressure gas using a vertical boat (wafer stacking jig), employs a device such as disclosed in Japanese Unexamined Patent Laid-Open Application No. 4-234119 (Prior art 3).
This device, although completely different from the device of the present invention in its application, is indicated as the prior art for reference because its construction is similar to that of the device of the invention. Prior art 3 is xe2x80x9ca device for treating semiconductor wafers characterized by comprising: a pressure vessel; a hollow body having a treatment chamber within the pressure vessel, the hollow body having a lower opening for receiving a plurality of wafers when the plurality of wafers are moved as a group from a position in a lower region of the pressure vessel to a position within the treatment chamber; operating means movable perpendicularly to the pressure vessel for closing the opening; means for introducing a high-pressure inert gas into the pressure vessel; means for beating an oxidizing agent within the treatment chamber; means for cooling the hollow body after the wafers have been processed within the treatment chamber; and means, coupled with the pressure vessel and the hollow body for equalizing the pressure of the inert gas and that of the oxidizing agent and coupled with a main body for equalizing the pressure of the inert gas and that of the oxidizing agent, for substantially separating the insert gas from the oxidizing agent.xe2x80x9d The wafers, which are the products to be treated, are treated while stored in a vertical boat that can stack several tens to one hundred and several tens of wafers thereon.
In the single wafer type devices, such as Prior arts 1 and 2, whose treatment mode is different from that of a so-called batch type device according to the present invention, problems inherent in their processing mode are more serious than drawbacks attributable to their structure.
That is, to meet the requirement that the cycle time of the single wafer processing be substantially equal to that of the concurrently performed PVD treatment, a short-cycle operation must be repeated more than tens of thousands of times per month.
In such a heavy-duty operation, various parts and components including the seal structure, seal material and the like of the opening and closing part of the vessel are used under so severe conditions that it would be quite difficult for these devices to secure safety and treatment reliability.
Especially, taking the pressure filling method for wiring films as an example, it is difficult to design a single wafer treatment device having a satisfactory life standing up to 1,000,000 or more operations for the following reasons. In the pressure filling method for wiring films, copper films are replacing conventional Al films in recent years, and the pressure filling method for these copper films require a high pressure of 100 MPa or more, or even 150 MPa at low temperatures of 350-400xc2x0 C. Due to such a high pressure involved in the process, it is difficult to design a single wafer treatment device with a satisfactory life.
Further, the high-pressure oxidation device such as Prior art 3 is operated with an inert gas unless an oxidizing agent is introduced. Since the device of this type is originally intended to perform an oxidation treatment, no considerations are given to air that inevitably enters into the high-pressure vessel when objects to be treated are put in and out of the vessel. That is, no such considerations are given at all since unlike the pressure filling method having to cope with the oxidation problem of wafers, the oxidation treatment requires no measures to prevent possible mixture of oxygen, i.e., mixture of oxygen accompanied by mixture of air. Therefore, this device addresses problems when operated in an almost inert atmosphere, especially in an oxygen-free atmosphere.
Under such prior art situation, a recent tendency is that wafers not only have larger diameter from 8 to 12 inches, but also are managed in a smaller lot size. In a standard fabrication process for 8 inches wafers, twenty-five wafers are stored in a single cassette, and product quality control is carried out on a lot basis, the size of a lot being 25, 50, or 100 wafers, i.e., multiples of 25.
However, the minimum lot size of twenty-five wafers is likely to change to, for example, thirteen as the wafer diameter increases to 12 inches. Particularly, the lot size will probably be decreased for the production of semiconductors applied to logic parts that are to be fabricated in small quantities and in various types. Under such circumstances, it is most likely that a device capable of flexibly accommodating various production quantities with a minimum lot size will dominate the future design of a fabrication device.
The above-mentioned single wafer treatment devices (Prior arts 1 and 2) could respond to this requirement. However, their structure of being integrated with a film-forming device used in the preceding step of sputtering rather imposes difficulty when they need to be operated with other film-forming methods, e.g., a plating method in combination.
To meet such needs, it is preferable to use a device or system capable not only of operating independently of the preceding and succeeding steps but also of treatment efficiently a small lot of one to ten or so wafers in accordance with the production quantity. However, such a device or system has not yet been proposed.
On the other hand, due to the fact that the formation of oxide films by oxidation is time-dependent, the oxidation treatment device such as shown as Prior art 3 inevitably requires much time for processing even a small lot of wafers. Thus, the device of this type has many problems to be overcome.
For treatment not so time-restricted as above, a device or system capable of processing a small lot of wafers quickly while maintaining a certain level of productivity can be constructed. It is known that a high-temperature and high-pressure treatment, such as the pressure filling method for wiring films, is less restrictive in terms of time.
Therefore, a device or system for such a high-temperature and high-pressure process must also meet the requirement for the small-lot processing. In this case, it is important to give a solution to the problem of how a minimum-sized device can handle wafers in what lot size. That is, the heart of the problem is how a device of small treatment capacity can treat a maximum number of wafers.
The present invention has been made in view of the above circumstances, and an object of the invention is therefore to provide a high-temperature and high-pressure treatment device for semiconductor wafers adapted for treating a comparatively small lot of wafers based on the fact that a high-temperature and high-pressure gas is subjected to natural convection quite easily and its temperature also tends to be easily homogenized.
The present invention further proposes a device for treating semiconductor wafers in a high-temperature and high-pressure inert atmosphere on a batch basis with about one to twenty-five wafers per batch. More particularly, the invention allows high-pressure treating to be effected with a high productivity while solving technical problems inherent in producing semiconductors, such as contamination of semiconductor wafers by particles and the like caused, for example, during the treatment step.
The present invention provides the following technical means in order to achieve the above objects.
That is, according to one aspect of the present invention, there is provided a high-temperature and high-pressure treatment device which is intended to treat semiconductor wafers in an atmosphere of high-temperature and high-pressure gas, and which includes: a pressure vessel having at a lower portion thereof an opening for putting the semiconductor wafers in and out; a lower lid disposed so as to be vertically movable for opening and closing the lower opening; wafer transfer means for stacking and unstacking the semiconductor wafers onto and from the lower lid; and a heater attached to the lower lid for heating the semiconductor wafers.
In a high-temperature and high-pressure treatment device, the heater could be disposed so as to surround the semiconductor wafers, which are the products to be treated, within the pressure vessel. Particularly, in the case where vertically stacked wafers are treated on a batch basis, it would generally be considered preferable to arrange the heater in that way in order to achieve a uniform temperature distribution in each wafer. However, such heater arrangement causes the pressure vessel to have a larger diameter.
The inventors have found that a non-uniform temperature distribution is hard to occur when a high-pressure gas is used because of its natural convection. Paying attention to this fact, the inventors decided to arrange the heater on the lower lid for the present invention.
That is, the fact that the heater is arranged on the lower lid means that the heater is located in a lower region of the pressure vessel. The heater so located causes an upflow due to its heat, and such an upflow together with violent natural convection currents of the high-pressure gas make the temperature within the pressure vessel substantially uniform. This heater arrangement of the present invention is particularly effective for a comparatively small lot production, and it also prevents the pressure vessel from having a larger diameter and thus contributes to downsizing the device.
Further, according to the invention, the lower lid is movable downward, and so is the heater that is disposed thereon, and thus the heater can be detachably arranged in and out of the pressure vessel. That is, by lowering the lower lid, the heater can be taken out of the pressure vessel together with the lower lid, and thus its maintenance becomes easier than a heater being fixed inside the pressure vessel.
Note that the heater may be disposed directly on the lower lid or indirectly through other members.
It is preferable that the heater have a substantially disc-like general form and be comprised of a plurality of radially split heating elements that can be controlled independently of each other.
Since this heater design allows the temperature distribution to be controlled in the radial direction, a further uniform temperature distribution can be achieved.
It is also preferable that: the pressure vessel have in an upper portion thereof a high-pressure gas introducing passage for introducing a high-pressure gas into a treatment chamber provided therein and a high-pressure gas discharging passage for discharging the high-pressure gas from the treatment chamber; the pressure vessel have therewithin a treatment chamber forming member for defining part of a space thereof as the treatment chamber for the semiconductor wafers; the gas introducing passage be formed so as to reach an inner surface of the treatment chamber forming member so that the gas can be supplied directly to an upper region of the treatment chamber; and the treatment chamber forming member have an opening at a lower portion thereof so that the gas discharged from the lower opening reaches the high-pressure gas discharging passage while passing through a space outside the treatment chamber forming member.
It is still further preferable that the lower lid has an independent gas discharging passage which opens to release the gas and particles within the pressure vessel while the pressure vessel is under low pressure or being evacuated.
It is still further preferable that the gas introducing passage have a stop valve for controlling gas flow and that a filter for entrapping particles be disposed downstream of the stop valve.
According to another aspect of the present invention, there is provided a high-temperature and high-pressure treatment device, which is intended to treat semiconductor wafers in an atmosphere of high-temperature and high-pressure gas and which includes: a pressure vessel; a treatment chamber for treating a plurality of stacked semiconductor wafers within the pressure vessel; a heater disposed within the treatment chamber so as to be located under the plurality of stacked semiconductor wafers; and a convection current passage forming member for forming a first passage and a second passage within the treatment chamber, the first passage having the semiconductor wafers therewithin and passing an upflow resulting from heating by the heater, the second passage communicating with the first passage at upper and lower regions of the treatment chamber and causing circulating convection currents to be formed between the first passage and itself by a downflow passing therethrough.
In the above construction, the heater is located under the semiconductor wafers, and such a construction prevents the pressure vessel from having a larger diameter compared with the case where the heater is disposed beside the semiconductor wafers.
Further, the convection current forming member is disposed in this construction in order to improve temperature uniformity within the treatment chamber. Therefore, the first passage causes an upflow due to the heat from the heater, and such an upflow enters into the second passage and becomes a downflow going down into the lower region of the treatment chamber and returning to the first passage, thereby forming in circulating convection currents throughout the first and second passages. Such circulating convection contributes to further improving temperature uniformity within the treatment chamber.
Further, it is preferable that temperature measuring means be disposed at the first passage.
Although a substantially uniform heat distribution can be achieved in a regular high-temperature and high-pressure operation, e.g., under a pressure as high as 20 MPa or more, it is still important to monitor the temperature throughout the whole operation in order to guarantee a specified temperature history of the semiconductor wafers. Further, there may be a case where large power must be supplied to the heater for an operation requiring heating at the time of low pressure. In such a case, to prevent overheating of the heater, it is recommended that a separate temperature measuring means be arranged near the heater so that temperatures near the heater can be monitored.
It is also preferable that the convection current passage forming member be a soaking cylindrical member which has openings at upper and lower portions thereof and which is disposed so as to surround the plurality of stacked semiconductor wafers, and that a space inside the cylindrical member serve as the first passage and a space outside the cylindrical member serve as the second passage.
In this case, due to heat from the heater, an upflow is caused within the soaking cylindrical member, and due to the upper and lower openings of the cylindrical member, a downflow is caused outside the cylindrical member. As a result, circulating convection currents are formed inside and outside the cylindrical member. Such circulating convection ensures a uniform heat distribution within the treatment chamber.
It is further preferable, in this case, that a shielding member be disposed between the cylindrical member and the lower inner surface of the pressure vessel. This arrangement prevents particles staying on the lower inner surface of the pressure vessel from entering into the passage.
According to still another aspect of the present invention, there is provided a high-temperature and high-pressure treatment device, which is intended to treat semiconductor wafers in an atmosphere of high-temperature and high-pressure gas and which includes: a pressure vessel; a treatment chamber for treating a plurality of stacked semiconductor wafers within the pressure vessel; a heater disposed within the treatment chamber so as to be located under the plurality of stacked semiconductor wafers; an airtight casing constructed so as to enclose the heater; a first gas passage formed within the airtight casing so that spaces inside and outside the airtight casing communicate with each other; and a filter deposed on the first gas passage for entrapping particles.
While various factors are responsible for the formation of particles within the pressure vessel, the heater is the most responsible one.
According to this construction, the heater that produces particles is enclosed in the casing, whereby the particles formed in the heater are prevented from contaminating the semiconductors.
Further, this device is a high-pressure device designed to be used under, for example, a maximum pressure of so high as 200 MPa, and the airtight casing, if not provided with a passage for communicating with the outside, will be broken due to pressure differences in and out. Thus, the first gas passage is provided in the airtight casing lest the casing should break. Further, the filter is also disposed in the casing lest particles should move together with the gas flowing in and out of the casing. Therefore, this arrangement of the present invention prevents breakage of the airtight casing while preventing contamination of the wafers within the pressure vessel.
It is preferable that the device comprise a second gas passage formed in the airtight casing so that spaces inside and outside the airtight casing communicate with each other, and that the second gas passage have a reverse flow preventing device allowing the gas to flow only into the airtight casing from outside.
With this arrangement, the gas enters into the casing mainly via the second gas passage, and exits from the casing mainly via the first gas passage. That is, the first gas passage, due to its having the filter disposed for entrapping particles, has a high air-flow resistance, and thus if only the first gas passage were provided, it would take much time for the gas to enter into the casing. However, since the second gas passage with no filter is disposed, the gas can enter the casing more quickly.
Additionally, the second gas passage has the reverse flow preventing device, and thus particles and the gas do not exit from the casing via the second gas passage. The gas flows out through the filter of the first gas passage, thereby preventing particles from going out of the casing. Moreover, since the gas passing through the filter flows only in the direction of going out of the casing, the gas is less likely to scatter the particles around.
It is also preferable that the airtight casing have a coupling opening to be coupled with an inner surface of the pressure vessel and the coupling opening be coupled with the inner surface of the pressure vessel so as to close the coupling opening substantially airtightly, and that an electric cable for supplying electricity to the heater from outside the pressure vessel be disposed so that the cable reaches the heater within the airtight casing while being extended by a distance allowing the inner surface of the pressure vessel to close the coupling opening.
According to this construction, the heater is enclosed by both the airtight casing and the inner surface of the pressure vessel. Further, the electrical cable is extended to the heater within the casing directly from the inner surface of the pressure vessel, and thus there is no need to pass the cable through the casing wall. Still further, the resultant simple structure ensures easy maintenance. It is also quite important that a semiconductor fabrication device implement quick maintenance.